Method of forming process film

ABSTRACT

A method of forming a process film includes the following operations. A substrate is transferred into a process chamber having an interior surface. A process film is formed over the substrate, and the process film is also formed on the interior surface of the process chamber. The substrate is transferred out of the process chamber. A non-process film is formed on the interior surface of the process chamber. In some embodiments, porosity of the process film is greater than a porosity of the non-process film.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of and claims the priority benefit ofU.S. application Ser. No. 15/925,785, filed on Mar. 20, 2018, nowallowed. The entirety of the above-mentioned patent application ishereby incorporated by reference herein and made a part of thisspecification.

BACKGROUND

In the fabrication of semiconductor integrated circuit (IC) devices,various device features such as insulation layers, metallization layers,passivation layers, etc., are formed on a semiconductor substrate. It isknown that the quality of an IC device fabricated is a function of theprocesses in which these features are formed. The yield of an ICfabrication process in turn is a function of the quality of the devicefabricated and a function of the cleanliness of the manufacturingenvironment in which the IC device is processed.

The ever increasing trend of miniaturization of semiconductor IC devicesrequires more stringent control of the cleanliness in the fabricationprocess and the process chamber in which the process is conducted. Inrecent years, contamination caused by particles or films has beenreduced by the improvements made in the quality of clean rooms and bythe increasing utilization of automated equipment which are designed tominimize exposure to human operators. However, even though contaminantsfrom external sources have been reduced, various contaminating particlesand films are still generated inside the process chamber during theprocessing of semiconductor wafers. Therefore, attention has been drawnto an effective chamber cleaning method.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the criticaldimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a schematic cross-sectional view of one embodiment of aprocess chamber in implementation of the present disclosure.

FIG. 2 is a flow chart of a method of cleaning a process chamber inaccordance with some embodiments.

FIG. 3A to FIG. 3F are schematic cross-sectional views of a method ofcleaning a process chamber in accordance with some embodiments.

FIG. 4 is a graph of sequence of pulses of different precursors inaccordance with some embodiments.

FIG. 5 is a flow chart of a method of cleaning a process chamber inaccordance with alternative embodiments.

FIG. 6 is a schematic cross-sectional view of a stage of a processchamber immediately before cleaning the process chamber in accordancewith some embodiments.

FIG. 7 is a schematic cross-sectional view of a stage of a processchamber immediately before cleaning the process chamber in accordancewith alternative embodiments.

FIG. 8 is a schematic cross-sectional view of a stage of a processchamber immediately before cleaning the process chamber in accordancewith yet alternative embodiments.

FIG. 9 is a flow chart of a method of cleaning a process chamber inaccordance with alternative embodiments.

FIG. 10 is a flow chart of a method of cleaning a process chamber inaccordance with yet alternative embodiments.

FIG. 11 is a graph of sequence of pulses of different precursors inaccordance with yet alternative embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a second feature over or on a first feature in the description thatfollows may include embodiments in which the second and first featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the second and first features,such that the second and first features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath”, “below”, “lower”,“on”, “over”, “overlying”, “above”, “upper” and the like, may be usedherein for ease of description to describe one element or feature'srelationship to another element(s) or feature(s) as illustrated in thefigures. The spatially relative terms are intended to encompassdifferent orientations of the device in use or step in addition to theorientation depicted in the figures. The apparatus may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

The present disclosure provides a novel method suitable for cleaning aprocess chamber. In some embodiments, the method of the presentdisclosure merely requires a single cleaning operation after multiplewafers are respectively deposited with process films in the chamber, andtherefore, the chamber cleaning time can be significantly reducedbecause no chamber cleaning step is required between the depositionsteps of two adjacent wafers.

More specifically, in some embodiments, the deposition step of anon-process film, instead of the conventional chamber cleaning step, isprovided between the deposition steps of two adjacent wafers. In someembodiments, a process film indicates a functional film or a target filmremained on a wafer, and a non-process film indicates a non-functionalfilm or a season film not required for a wafer. When a process film isdeposited on a wafer in a process chamber, the process film is alsodeposited on the interior surface of the process chamber. Morespecifically, a process film is deposited on the interior chambersurface when a wafer is processed in the chamber. On the contrary, anon-process film is deposited on the interior chamber surface when awafer is not present in the chamber. In the process chamber, thenon-process film is formed over the adjacent process film so as toadhere the process film to the interior surface and therefore preventthe films from contaminating a wafer that is being processed in thechamber. After multiple wafers are respectively deposited with processfilms in the chamber, the undesired process films and non-process filmsare removed from the interior surface of the process chamber by anextended cleaning operation.

FIG. 1 is a schematic cross-sectional view of one embodiment of aprocess chamber in implementation of the present disclosure.

Referring to FIG. 1, a process chamber 10 may be used to deposit variousmaterial layers, such as low-k dielectric films, on multiplesemiconductor wafers. It is understood that the process chamber 10 shownin FIG. 1 is merely one example of a CVD process chamber which issuitable for implementation of the present disclosure. Accordingly, themethod of the present disclosure may be used to clean other processchambers having features which differ from those of the process chamber10 shown in FIG. 1. For example, the method of the present disclosuremay be used to clean an atomic layer deposition (ALD) process chamber.

In some embodiments, the process chamber 10 includes a chamber housing100 which contains a wafer support pedestal 150. A heater element 170may be embedded in the wafer support pedestal 150 for heating a wafersupported on the wafer support pedestal 150. An AC power supply 106 istypically connected to the heater element 170. A temperature sensor 172is typically embedded in the wafer support pedestal 150 to monitor thetemperature of the pedestal 150. The measured temperature is used in afeedback loop to control the power supplied to the heater element 170through the AC power supply 106.

In some embodiments, the process chamber 10 further includes a gasdistribution plate or a showerhead 120 provided in the top of thechamber housing 100. The showerhead 120 is configured for theintroduction of process gases into the chamber housing 100. A gas panel130, which is used to select the gases to be introduced into the chamber10 through the showerhead 120, is connected to the showerhead 120. Avacuum pump 102 is operably connected to the chamber housing 100 tomaintain proper gas flow and pressure inside the chamber housing 100, aswell as to evacuate reactant by-products from the chamber housing 100.

A control unit 110 is operably connected to the gas panel 130 and to thevarious operational components of the chamber housing 100, such as thevacuum pump 102 and the AC power supply 106, to control a CVD processcarried out in the chamber housing 100. Control of process gases flowingthrough the gas panel 130 is facilitated by mass flow controllers (notshown) and a microprocessor controller (not shown). In a CVD process,the showerhead 120 facilitates a uniform distribution of process gasesover the surface of a wafer W supported on the wafer support pedestal150.

The showerhead 120 and the wafer support pedestal 150 form a pair ofspaced-apart electrodes in the chamber housing 100. When an electricfield is generated between these electrodes, the process gases flowinginto the chamber housing 100 through the showerhead 120 are ignited toform a plasma. Typically, the electric field is generated by connectingthe wafer support pedestal 150 to a source of RF (radio frequency) powerthrough a matching network (not shown). Alternatively, the RF powersource and the matching network may be coupled to the showerhead 120 orto both the showerhead 120 and the wafer support pedestal 150.

A remote plasma source 180 may be coupled to the chamber housing 100 toprovide a remotely-generated plasma to the chamber housing 100. Theremote plasma source 180 includes a gas supply 153, a gas flowcontroller 155, a plasma chamber 151 and a chamber inlet 157. The gasflow controller 155 controls the flow of process gases from the gassupply 153 to the plasma chamber 151.

A remote plasma may be generated by applying an electric field to theprocess gas in the plasma chamber 151, creating a plasma of reactivespecies. Typically, the electric field is generated in the plasmachamber 151 using an RF power source (not shown). The reactive speciesgenerated in the remote plasma source 180 are introduced into thechamber housing 100 through the inlet 157.

During the operation of the process chamber 10, when a material layer103 a is deposited over a wafer W supported on the wafer supportpedestal 150, material residues 103 b gradually accumulate on theinterior surface S of the process chamber 10. The interior surface S ofthe process chamber 10 includes surfaces of elements exposed to thereaction gases or precursors. In some embodiments, the interior surfaceS includes the surface S1 of the chamber housing 100 and the surface S2of the showerhead 120. Particles from the material residues 103 b have atendency to break off and potentially contaminate devices beingfabricated on subsequent wafers processed in the process chamber 10, andtherefore, must be periodically removed from the interior surface S foroptimum processing.

FIG. 2 is a flow chart of a method of cleaning a process chamber inaccordance with some embodiments. FIG. 3A to FIG. 3F are schematiccross-sectional views of a method of cleaning a process chamber inaccordance with some embodiments. FIG. 4 is a graph of sequence ofpulses of different precursors in accordance with some embodiments. Insome embodiments, the chamber cleaning method is applied to, for examplebut not limited to, the process chamber 10 of FIG. 1, in which someelements are omitted for the sake of clarity and convenience.

Referring to FIG. 2 and FIG. 3A, in step 202, a substrate or a wafer Wis transferred into a process chamber 10 having an interior surface S.In some embodiments, in step 202, no precursor is introduced into theprocess chamber 10, as shown in FIG. 4.

Referring to FIG. 2 and FIG. 3B, in step 204, a process film P₁ isformed over the substrate or the wafer W, and the process film P₁ isalso deposited on the interior surface S of the process chamber 10. Insome embodiments, in step 204, a first precursor 310 and a secondprecursor 320 are introduced into the process chamber 10 for a firsttime period t1, as shown in FIG. 4. In some embodiments, the firstprecursor is a film forming precursor or a dielectric matrix precursor,and the second precursor is a pore forming precursor or a porogenprecursor. In some embodiments, the film forming precursor can be asilicon-rich precursor including methyldiethoxysilane (MDEOS) ordiethoxymethylsilane (DEMS), and the pore forming precursor can be acarbon-rich precursor including alpha-terpinene (ATRP), ethylene (C₂H₄)or a chemical corresponding to the general formula(CH₃)₂CHC₆H₆—C_(n)H_(2n+1) (n is a positive integer).

In some embodiments, the process film P₁ is a porous organosilicateglass (OSG) film deposited using a DEMS structure forming precursor andan ATRP pore forming precursor. In some embodiments, the process film P₁is a porous low-k layer having a dielectric constant of about 3.0 orless, about 2.6 or less, or about 2.0 or less.

Referring to FIG. 2 and FIG. 3C, in step 206, the substrate or the waferW is transferred out of the process chamber 10. In some embodiments, instep 206, no precursor is introduced into the process chamber 10, asshown in FIG. 4.

Referring to FIG. 2 and FIG. 3D, in step 208, a non-process film NP₁ isdeposited on the interior surface S of the process chamber 10.Specifically, the non-process film NP₁ is deposited over the processfilm P₁ on the interior surface S of the process chamber 10, so as toadhere the process film P₁ to the interior surface S and thereforeprevent the films from contaminating a wafer that is being processed inthe chamber. In some embodiments, in step 208, the second precursor 320is not introduced into the process chamber 10, while the first precursor310 is introduced into the process chamber 10 for a second time periodt2, as shown in FIG. 4. In some embodiments, the first time period t1 isdifferent from (e.g., greater than) the second time period t2, but thedisclosure is not limited thereto. In alternative embodiments, the firsttime period t1 is substantially the same as the second time period t2.In some embodiments, the process film P₁ and the non-process film NP₁are formed at the same process chamber temperature.

In some embodiments, the non-process film NP₁ is a substantiallynon-porous organosilicate glass (OSG) film deposited using a DEMSstructure-former precursor. In some embodiments, the non-process filmNP₁ has a dielectric constant greater than that of the process film P₁.In some embodiments, the non-process film NP₁ has a dielectric constantof more than about 2.6, and preferably more than about 3.0.

Thereafter, in step 210, the process chamber 10 is idled for an idletime period before the next substrate or wafer is transferred into aprocess chamber 10. In some embodiments, in step 210, no precursor isintroduced into the process chamber 10, as shown in FIG. 4.

Referring to FIG. 2 and FIG. 3E, in step 212, step 202 to step 210 arerepeated m times, where m is an integer between 1 and 25, between 3 and13, or between 6 and 10. In some embodiments, m indicates the number ofwafers processed in the process chamber 10. After m wafers are processedin the process chamber 10, process films P₁ to P_(m) and non-processfilms NP₁ to NP_(m) are alternately deposited on the interior surface Sof the process chamber 10. In some embodiments, the process films P₁ toP_(m) and the non-process films NP₁ to NP_(m) constitute a film stack FSon the interior surface S of the process chamber 10.

In some embodiments, step 202 to step 210 constitute a deposition cycle400 of the process chamber 10. Multiple deposition cycles 400 areperformed until the predetermined number of wafers are respectivelycompleted with their deposition steps. In some embodiments, there is nocleaning step between any two of step 202 to step 212. In someembodiments, there is no cleaning step in the repeating step 212.

Referring to FIG. 2 and FIG. 3F, in step 214, a cleaning operation isperformed to remove the process films P₁ to P_(m) and the non-processfilms NP₁ to NP_(m) from the interior surface S of the process chamber10. In some embodiments, the cleaning gas for the cleaning operationincludes a fluorine source. The fluorine source includes NF₃, F₂, SF₆,CF₄, C₂F₆, C₃F₈ or a combination thereof. In some embodiments, thecleaning gas for the cleaning operation further includes an inert gas,such as argon, helium or a combination thereof.

In the present disclosure, the deposition step of a non-process film,instead of the conventional chamber cleaning step, is provided betweenthe deposition steps of process films of two adjacent wafers. Thenon-process film helps to adhere the underlying process film to theinterior surface of the process chamber, and therefore prevents the filmstack from peeling and contaminating a wafer that is processed in thechamber. The method of the present disclosure merely requires a singlecleaning operation after multiple wafers are respectively deposited withprocess films in the chamber, and therefore, the chamber cleaning timecan be significantly reduced.

In some embodiments, the present disclosure further provides a method ofcleaning a process chamber as shown in FIG. 5 with reference to FIG. 4and FIGS. 6-8.

Referring to FIG. 4 and FIG. 5, step (a) of introducing a firstprecursor 310 and a second precursor 320 into a process chamber 10 for afirst time period t1 and step (b) of introducing the first precursor 310into the process chamber 10 for a second time period t2 are repeatedalternately m times (m is an integer between 1 and 25), and a film stackis built up on an interior surface S of the process chamber 10 afterstep (a) and step (b) are repeated m times. In some embodiments, thefilm stack includes process films and non-process films alternativelystacked on the interior surface S of the process chamber 10.

In some embodiments, step (a) is first performed in the repeating step,and the film stack FS built up on an interior surface S of the processchamber 10 is shown in FIG. 6. Specifically, a process film P₁ is firstformed in the repeating step and is in contact with the interior surfaceS of the process chamber 10.

In alternative embodiments, step (a) is last performed in the repeatingstep, and the film stack FS built up on an interior surface S of theprocess chamber 10 is shown in FIG. 7. Specifically, a process filmP_(m) is last formed in the repeating step. After the process film P_(m)is formed, the wafer is transferred out of the process chamber, and theprocess chamber is then immediately subjected to a cleaning operation.

In yet alternative embodiments, step (b) is first performed in therepeating step, and the film stack FS built up on an interior surface Sof the process chamber 10 is shown in FIG. 8. Specifically, anon-process film is first formed in the repeating step and is in contactwith the interior surface S of the process chamber 10.

After multiple wafers are respectively deposited with their processfilms in the same chamber, as shown in step (c) of FIG. 5, a cleaningoperation is performed to remove the film stack (as shown in FIG. 6,FIG. 7 or FIG. 8) from the interior surface S of the process chamber 10.In some embodiments, the cleaning gas for the cleaning operationincludes a fluorine source, an inert gas or a combination thereof.

In some embodiments, the present disclosure also provides a method ofcleaning a process chamber as shown in FIG. 9 with reference to FIG. 4and FIGS. 6-8.

Referring to FIGS. 6-9, in step (i), a plurality of process films and aplurality of non-process films are formed alternately on an interiorsurface S of the process chamber 10.

In some embodiments, as shown in FIG. 4, the method of forming theprocess films and the non-process films includes introducing firstpulses 312 and 314 of a first precursor 310 into the process chamber 10,and introducing second pulses 322 of a second precursor 320 into theprocess chamber 10. In some embodiments, the first pulses 312 and 314 ofthe first precursor 310 partially overlap with the second pulses 322 ofthe second precursor 320. For example, the first pulses 312 of the firstprecursor 310 overlapping with the second pulses 322 of the secondprecursor 320 and the first pulses 314 of the first precursor 310 notoverlapping with the second pulses 322 of the second precursor 320 arearranged alternately. In some embodiments, the first precursor 310 is afilm forming precursor, and the second precursor 320 is a pore formingprecursor. In some embodiments, the process chamber temperature keepsconstant during the formation of the process films and the non-processfilms.

In some embodiments, the dielectric constant of the process films isdifferent from (e.g., less than) the dielectric constant of thenon-process films. In some embodiments, the dielectric constant of theprocess films is about 3.0 or less, and the dielectric constant of thenon-process films is greater than about 3.0 and less than about 4.0. Inalternative embodiments, the dielectric constant of the process films isabout 2.5 or less, and the dielectric constant of the non-process filmsis greater than about 2.5. In yet alternative embodiments, thedielectric constant of the process films is about 2.0 or less, and thedielectric constant of the non-process films is greater than about 2.0.

In some embodiments, the porosity of the process films is different from(e.g., greater than) the porosity of the non-process films. In someembodiments, the process films are porous dielectric layers, and thenon-process films are pore-free dielectric layers.

In some embodiments, the process films have a stress different from(e.g., greater than) the stress of the non-process films. In someembodiments, the process films are tensile dielectric layers, and thenon-process films are compressive dielectric layers. The non-processfilms help to relieve the stress of the process films on the interiorsurface of the process chamber.

In some embodiments, a process film and a non-process film adjacent tothe process film are in a thickness ratio of about 1:1 to 10:1. Forexample, the process film and the non-process film adjacent to theprocess film are in a thickness ratio of about 3:1 to 4:1. Bycontrolling and adjusting the above thickness ratio within the range ofthe disclosure, the film stack can be stably adhered to the interiorchamber surface before a chamber cleaning operation, and can be easilyremoved during the chamber cleaning operation.

After multiple wafers are respectively deposited with their processfilms in the same chamber, as shown in step (ii) of FIG. 9, a cleaningoperation is performed to remove the process films and the non-processfilms from the interior surface S of the process chamber 10. In someembodiments, the cleaning gas for the cleaning operation includes afluorine source, an inert gas or a combination thereof.

The above embodiments in which two precursors are used in the chambercleaning process are provided for illustration purposes, and are notconstrued as limiting the present disclosure. In some embodiments, morethan two precursors can be used in the chamber cleaning process.

In some embodiments, the present disclosure further provides a method ofcleaning a process chamber as shown in FIG. 10 and FIG. 11.

Referring to FIG. 10 and FIG. 11, step (a) of introducing a firstprecursor 310, a second precursor 320 and a third precursor 330 into aprocess chamber 10 for a first time period t1 and step (b) ofintroducing the first precursor 310 into the process chamber 10 for asecond time period t2 are repeated alternately m times (m is an integerbetween 1 and 25), and a film stack is built up on an interior surface Sof the process chamber 10 after step (a) and step (b) are repeated mtimes. In some embodiments, the film stack includes process films andnon-process films alternatively stacked on the interior surface S of theprocess chamber 10.

Specifically, the method of forming the process films and thenon-process films includes introducing first pulses 312 and 314 of afirst precursor 310 into the process chamber 10, introducing secondpulses 322 of a second precursor 320 into the process chamber 10, andintroducing third pulses 332 of a third precursor 330 into the processchamber 10. In some embodiments, the first pulses 312 and 314 of thefirst precursor 310 partially overlap with the second pulses 322 of thesecond precursor 320 and the third pulses 332 of the third precursor330. For example, the first pulses 312 of the first precursor 310overlapping with the second/third pulses 322/332 of the second/thirdprecursor 320/330 and the first pulses 314 of the first precursor 310not overlapping with the second/third pulses 322/332 of the second/thirdprecursor 320/330 are arranged alternately. In some embodiments, thefirst precursor 310 is a film forming precursor, the second precursor320 is a pore forming precursor, and the third precursor 330 is anotherpore forming precursor. In some embodiments, the first precursor 310 canbe a silicon-rich precursor including methyldiethoxysilane (MDEOS) ordiethoxymethylsilane (DEMS), and each of the second precursor 320 andthe third precursor 330 can be a carbon-rich precursor includingalpha-terpinene (ATRP), ethylene (C₂H₄) or a chemical corresponding tothe general formula (CH₃)₂CHC₆H₆—C_(n)H_(2n+1) (n is a positiveinteger).

After multiple wafers are respectively deposited with their processfilms in the same chamber, as shown in step (c) of FIG. 10, a cleaningoperation is performed to remove the film stack from the interiorsurface S of the process chamber 10. In some embodiments, the cleaninggas for the cleaning operation includes a fluorine source, an inert gasor a combination thereof.

In view of the above, in the present disclosure, the deposition step ofa non-process film, instead of the conventional chamber cleaning step,is provided between the deposition steps of process films of twoadjacent wafers. The non-process films help to adhere the process filmsto the interior surface of the process chamber, and therefore preventthe film stack from peeling and contaminating a wafer that is processedin the chamber. After multiple wafers are respectively deposited withtheir process films in the same chamber, an extended cleaning operationis performed to completely remove the process films and non-processfilms from the interior surface of the process chamber. By such manner,the chamber cleaning time is significantly reduced, and the volume orthroughput of wafers is greatly increased.

In accordance with some embodiments of the present disclosure, a methodof cleaning a process chamber includes the following steps. A pluralityof process films and a plurality of non-process films are alternatelyformed on an interior surface of the process chamber. A cleaningoperation is performed to remove the plurality of process films and theplurality of non-process films from the interior surface of the processchamber.

In accordance with alternative embodiments of the present disclosure, amethod of cleaning a process chamber includes the following steps. Step(a) of introducing a first precursor and a second precursor into aprocess chamber for a first time period and step (b) of introducing thefirst precursor into the process chamber for a second time period arerepeated alternately m times, wherein m is an integer between 1 and 25,and a film stack is built up on an interior surface of the processchamber after step (a) and step (b) are repeated m times. A cleaningoperation is then performed to remove the film stack from the interiorsurface of the process chamber.

In accordance with yet alternative embodiments of the presentdisclosure, a method of cleaning a process chamber includes thefollowing steps. A substrate is transferred into a process chamberhaving an interior surface. Thereafter, a process film is deposited overthe substrate, wherein the process film is also deposited on theinterior surface of the process chamber. Afterwards, the substrate istransferred out of the process chamber. Next, a non-process film isdeposited on the interior surface of the process chamber. The abovesteps are repeated m times, where m is an integer between 1 and 25. Acleaning operation is then performed to remove the process films and thenon-process films from the interior surface of the process chamber.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of forming a process film, comprising:(1) transferring a substrate into a process chamber having an interiorsurface; (2) forming a process film over the substrate, wherein theprocess film is also formed on the interior surface of the processchamber; (3) transferring the substrate out of the process chamber; and(4) forming a non-process film on the interior surface of the processchamber, wherein a porosity of the process film is greater than aporosity of the non-process film.
 2. The method of claim 1, whereinforming the process film comprises: introducing a first precursor intothe process chamber; and introducing a second precursor into the processchamber.
 3. The method of claim 2, wherein forming the non-process filmcomprises: continuing introducing the first precursor into the processchamber; and stopping introducing the second precursor into the processchamber.
 4. The method of claim 1, wherein a process chamber temperaturekeeps constant when forming the process film and the non-process film.5. The method of claim 1, wherein the process chamber is a chemicalvapor deposition (CVD) process chamber.
 6. The method of claim 1,wherein the process chamber is an atomic layer deposition (ALD) processchamber.
 7. The method of claim 1, wherein the process film and thenon-process film are in a thickness ratio of 1:1 to 10:1.
 8. A method offorming a process film, comprising: (1) transferring a substrate into aprocess chamber having an interior surface; (2) introducing a filmforming precursor and a pore forming precursor into the process chamberfor a first time period, so as to form a process film over thesubstrate, wherein the process film is also formed on the interiorsurface of the process chamber; (3) transferring the substrate out ofthe process chamber; (4) introducing the film forming precursor into theprocess chamber for a second time period; and (5) repeating (1)-(4) atleast one time, wherein the film forming precursor comprises asilicon-rich precursor, and the pore forming precursor comprises acarbon-rich precursor.
 9. The method of claim 8, wherein thesilicon-rich precursor comprises methyldiethoxysilane (MDEOS) ordiethoxymethylsilane (DEMS).
 10. The method of claim 8, wherein thecarbon-rich precursor comprises alpha-terpinene (ATRP), ethylene (C₂H₄)or a chemical corresponding to a general formula(CH₃)₂CHC₆H₆—C_(n)H_(2n+1), wherein n is a positive integer.
 11. Themethod of claim 8, wherein the process film is a porous organosilicateglass (OSG) film.
 12. The method of claim 8, wherein the non-processfilm is a substantially non-porous organosilicate glass (OSG) film. 13.The method of claim 8, further comprising introducing another poreforming precursor into the process chamber in step (2).
 14. The methodof claim 8, wherein the process chamber is a chemical vapor deposition(CVD) process chamber.
 15. The method of claim 8, wherein the processchamber is an atomic layer deposition (ALD) process chamber.
 16. Themethod of claim 8, wherein the first time period is different from thesecond time period.
 17. A method of forming a process film, comprising:(1) transferring a substrate into a process chamber having a showerhead;(2) forming a process film over the substrate, wherein the process filmis also formed on the showerhead of the process chamber; (3)transferring the substrate out of the process chamber; (4) forming anon-process film on the showerhead of the process chamber; and (5)repeating (1)-(4) m times to form the process films and the non-processfilms alternately, where m is an integer between 1 and 25, wherein aporosity of the process films is greater than a porosity of thenon-process films.
 18. The method of claim 17, wherein the processchamber is a chemical vapor deposition (CVD) process chamber.
 19. Themethod of claim 17, wherein the process chamber is an atomic layerdeposition (ALD) process chamber.
 20. The method of claim 17, wherein adielectric constant of the plurality of process films is 3.0 or less.